Due to the constant increase in power of high-voltage electric grids, it is often observed that in some cut-out units, fault currents can rapidly exceed the cut-out or holding capacities of their equipment.
To prevent this, known solutions which immediately come to mind consist in:
using new equipment which has higher cut-out and holding capacity, which leads to old equipment being replaced by expensive new equipment; PA1 dividing up the sets of bus bars, opening the lines, cutting up the grid into sub units so as to reduce the short-circuit current to an acceptable level--a solution which users dislike, since their systems no longer operate in optimum conditions; and PA1 using series impedances; this solution leads to extra constraints during transients for circuit-breakers and to voltage regulation problems requiring bulky equipment and entailing loss. PA1 have an extremely rapid operation time, of about two to three milliseconds; PA1 be able to limit the peak of the first large asymmetrical wave to a level compatible with the short-circuit holding capacity of the equipment; PA1 by inserting an impedance in the circuit, reduce the initial short-circuit current to a level which allows cutting out by existing conventional circuit-breakers which have insufficient cutting-out power; and PA1 have a sufficiently high rated current. PA1 interruption of the short-circuit current before its peak in a vacuum chamber by cancelling the magnetic field which is necessary for the movement of electrons in the arc column, the current then transiting via a resistor which allows the current to be reduced to a predetermined level, PA1 rapid cancellation of the current by injecting a large high-frequency current in the reverse direction, the device being able to cut out the current at the first artificial zero crossing before the first peak of the asymmetrical wave; and PA1 very energetic quenching by generating in a very short time an arcing voltage greater than the grid voltage, the arcing voltage reducing the amplitude of the short-circuit current and forcing it to pass through zero.
The required solution is a device which allows the short-circuit current to be reduced very rapidly to a predetermined level and which then allows the initial operating conditions to be re-established once the fault has been corrected.
Such a device must meet the following requirements:
The means which can be used for high voltage are based on the following principles:
With very high currents at high voltages, these principles come up against problems which are difficult to solve to meet the above requirements simultaneously.
The invention aims to provide a device which makes it possible to meet these requirements simultaneously.